1. Technical Field
The present invention relates to a polarizing plate, other optical devices, a projection-type imaging apparatus using such an optical device, and a method for producing an optical device.
2. Related Art
A projection-type imaging apparatus such as a liquid crystal projector is configured such that light from a light source is modulated by a light modulator according to image information to be projected and the light modulated by the light modulator is projected by a projection optical device. A polarizing plate is disposed between this light modulator and the light source.
In the related art, as the polarizing plate, there has been disclosed a polarizing plate obtained by bonding a polarizing film to glass (JP-A-10-039138). In JP-A-10-039138, as the polarizing film, for example, a polarizing film including iodine or a dichroic dye as a polarizer and a transparent polyvinyl alcohol (PVA) film as a substrate is disclosed, and the polarizing film has a thickness of 10 to 50 μm, more preferably about 25 to 35 μm. As the polarizing film, a so-called H film formed by stretching a PVA thin film while heating and immersing the film in a solution called an H ink containing a large amount of iodine (potassium iodide) to allow the film to absorb iodine, a film formed by allowing a polyvinyl butyral film to absorb iodine, a film formed by allowing a uniaxially stretched PVA film to absorb a dichroic dye, or the like is used.
Further, there has been disclosed a polarizing plate in which a bonding agent layer is formed on each of inner surfaces facing each other of transparent substrates facing and spaced apart from each other, and a polarizer composed of PVA or the like is provided on one of these bonding agent layers, and a retardation film is provided on the other bonding agent layer, and the polarizer and the retardation film are bonded to each other through a bonding agent layer, and exposed portions of the polarizer and the retardation film, which are not in contact with the bonding agent layers are sealed with a sealant (JP-A-2010-117537).
Further, there has been proposed a method for producing a polarizing plate in which transparent substrates are directly bonded to both surfaces of a polarizer with a bonding agent, wherein in order to prevent the occurrence of external shape abnormality such as wrinkles, a transparent substrate is bonded to one surface of a polarizer composed of PVA or the like with a bonding agent, followed by heating under pressure, and then, a transparent substrate is bonded to the other surface of the polarizer with a bonding agent (JP-A-2010-191203).
Recently, in a liquid crystal projector, the output of a white light source lamp is increased and an arc length is decreased, and therefore, a thermal load to each optical device mounted in an optical engine is being increased. An optical device in the related art cannot withstand light of a high luminance lamp and is deteriorated, resulting in decreasing the optical properties such as transmittance. Alternatively, a problem arises that an optical device made of a resin, a bonding agent, or the like is deformed due to heat.
That is, a polarizer made of, as a raw material, an organic film disclosed in JP-A-10-039138, JP-A-2010-117537, or JP-A-2010-191203 has a problem that a defect such as yellow discoloration due to light resulting from increasing the output or decreasing the arc length or heat generated by the light is caused.
Therefore, in the related art, there has been proposed a bonded article which includes: a first adherend having a first substrate and a first bonding layer which is formed by a plasma polymerization method on the first substrate, contains a structure of siloxane (Si—O) and having a crystallinity of 45% or less and also contains a leaving group which is composed of an organic group and binds to this structure of siloxane; and a second adherend having a second substrate and a second bonding layer which is formed by a plasma polymerization method on the second substrate, and has the same structure as the first bonding layer, wherein the first adherend and the second adherend are bonded to each other by a bonding property exhibited in each of a region on a surface of the first bonding layer and a region on a surface of the second bonding layer by applying energy to each of a region of at least a part of the first bonding layer and a region of at least a part of the second bonding layer so as to release the leaving group present in the vicinity of at least the surface of the first bonding layer and the second bonding layer from the structure of siloxane (Japanese Patent No. 4337935).
Further, in the related art, there has been proposed a polarizing plate formed by bonding a glass substrate to a polarizing film using the bonding layer proposed in Japanese Patent No. 4337935 (JP-A-2009-098465). The polarizing plate proposed in JP-A-2009-098465 includes a light transmissive substrate, a polarizing layer, and a bonding layer which bonds the substrate to the polarizing layer, and has a configuration such that the bonding layer contains a structure of siloxane which has an atomic structure containing a siloxane (Si—O) bond and a leaving group which binds to the structure of siloxane, and the bonding layer bonds the substrate to the polarizing layer by a bonding property exhibited in a region on a surface of the bonding layer by applying energy to a region of at least a part of the bonding layer so as to release the leaving group present in the vicinity of the surface of the bonding layer from the structure of siloxane.
Further, there has been proposed a laminated wave plate formed by bonding two quartz substrates to each other using the bonding layer described in Japanese Patent No. 4337935 in the same manner (JP-A-2009-258404).
Therefore, the present inventors tried to realize a polarizing plate having extremely high light resistance using the bonding layer proposed in Japanese Patent No. 4337935, JP-A-2009-098465, or JP-A-2009-258404 while using an organic film as a material of a polarizing device.
However, it was found that when a plasma-polymerized film is used as the bonding layer, the thickness of the bonding layer is several tens nanometers, for example, in the case of Japanese Patent No. 4337935, an extremely thin film having a thickness of 1 to 10000 nm, preferably 2 to 800 nm is used, and therefore, in the case where both principal surfaces of a film polarizer are sandwiched by inorganic light transmissive substrates, the irregularities of the surface of the film polarizer cannot be completely absorbed because the bonding layer is thin, and therefore, air bubbles and the like are incorporated to cause an external appearance defect, resulting in causing an adverse effect on the optical properties such as transmissibility. For example, PVA has a hygroscopic property and swells or shrinks depending on the humidity, and therefore, the film polarizer and the light transmissive substrates may be detached from each other.
Further, since the bonding layer is formed on both principal surfaces of the film polarizer by a plasma polymerization method, the time of exposure of the film polarizer to heat generated by a plasma is long, and therefore, a problem arises that the film polarizer itself is deteriorated or deformed.